1. Field of the Invention
The present invention relates to endless belts for battery pasting machines and to a method for manufacturing the same.
More particularly, the present invention relates to endless belts for pasting machines of electric lead battery plates.
2. Description of the Prior-art
In the industry of the electric lead batteries, the plates are produced by pasting an active material formed by a mixture of lead-oxide and bonding agents inside thin lead-alloy frames, called grids.
The grids are carried under the pasting machine hopper by a conveyor belt which is supported by a steady steel plate. The active material coming out from the hopper is pressed into the running grids by means of pressure rolls and uniformly distributed so that the pasted grids have a constant thickness.
For this purpose it is necessary that the belt facilitates the active material distribution inside the grid holes so that the lead-oxide material can stick accurately to the grid frames.
The ratio between the quantity of water inside the belt and that inside the active material has a great importance in order to create thin water films with lubricating purposes.
Heavy cotton belts are generally used as the most convenient grid conveying system.
Generally these cotton belts are woven 6-ply open-ended bands transformed into endless rings by joining the two band ends and seaming them together.
In order to guarantee the belt mechanical strength and to avoid elongations as well as a fast surface wearing, the band is woven with strong cotton yarns, for example count 700 to 900 decitex, strands 4 to 8 and 1.5 to 2.5 twists per cm.
The band weaving takes place with heavy shuttle looms equipped with 12 head shafts and 2 warp beams.
This band has a thickness of 6-7 mm. and a weight of about 4000/5000 gms/m.sup.2. Because of their remarkable thickness and their great number of length-wise and cross-wise yarns, these belts cannot be endlessly woven in the loom.
Therefore to get a ring-shaped belt from the band it is necessary to sew the two band ends after cutting it at the right length.
The seam is the most delicate and weak zone of these belts.
Since the seam zone must have the same thickness as the rest of the belt, the two band ends are sharpened in their thickness at decreasing sections so as to form a narrow angle over a rather wide area.
The two sharpened ends are put one upon the other and joined together by means of a suitable glue and are then sewn together to increase the stretching resistance of this zone.
Even though the thickness is constant throughout the entire belt, the seam area has a stiffness which is somehow different from the other points of the belt and its extensibility is far from being equal to the rest of the belt, thus creating some drawbacks.
One of these drawbacks is that, because of their cotton-yarn construction, the belt cannot be conveniently heat-set. The result is a lack of dimensional stability during the operation on the pasting machines.
The cotton belts, which are wetted during operation, tend to lengthen beyond the machine maximum stretching gauge, slipping around the driven and guide rolls of the pasting machine. Moreover, the seam or splice represents the weak point of the belt because both of the tension applied to it during working and the friction due to pasting machine pressure rolls and of the abrasion of the active material used for grid filling. The thin threads usually used for the belt seam are cut and the seam loses its strength. Another drawback of the known belts is that the joining of the two ends is rarely made at right-angle and therefore, the resulting belt is not perfectly cylindrical, but conical.
Conical belts tend to slip during operation from one side of the machine to the other or to move always towards the same machine side with damage for the belt edges.
Usually the belt edge wearing is the beginning of the seam break-up.
A further drawback of the known belts is that, because of the gluing agents, the water absorption in the seam area is different (lower) from the rest of the belt; consequently the distribution of the active material onto the grids is not uniform throughout the belt. Moreover, the belt thickness in the seam area is not equal to the rest of the belt; so that an irregular pasting occurs.